As hard as it is to believe, it is currently cheaper to travel halfway around the world, fight terrorists or buy off governments, drill miles below the earth's surface, pump the crude up and out to ships, truck it back to the US, put it through an amazingly complex and stinky chemical process, put it tank trucks and on to the tanks at your local gas station.........than it is to swirl waste grease together with methanol and lye and skim the biodiesel layer off once it settles. Oh sure, the biodiesel is cheaper if you're homebrewing batches of it, but commercial straight ASTM standard biodiesel is $3.00 a gallon or more.

I think that will eventually change as the economies of scale come to bear on biodiesel production and/or someone figures out ways to make it even more efficient. But for now, commercial biodiesel is something you buy because it feels like the right thing to do, not because it's cheaper.

B20 (20% biodiesel, 80% petrodiesel) at a pump seems to cost about 20 cents a gallon more than regular petrodiesel. The energy bill that's been stuck in Congress for 4 years has a provision to cut the excise tax by 20 cents on B20. That would at least make it cost around the same as petrodiesel at the pump, which might spur on greater acceptance of it. If that bill ever passes, which doesn't look likely.

Duncan